Emerging evidence suggests a critical role for dendritic cells (DCs) in maintaining the balance between immunity to pathogens versus immune tolerance to self antigens. However the intracellular signaling networks and transcription factors that program DCs to induce tolerogenic responses are poorly understood. In this context, work performed during the previous cycle of this grant has identified two novel signaling mechanisms in DCs that induce T regulatory responses: (i) TLR2 mediated activation of ERK MAP kinase which mediates the production of anti-inflammatory mediators such as IL-10 and the retinoic acid metabolizing enzymes (RALDH2), thus programming the DCs to induce T regulatory cells. (ii) TLR-mediated induction of the wnt-?? -catenin signaling axis in splenic DCs, which also facilitates induction of IL-10 and RALDH2, again, programming a tolerogenic state. Strikingly, our preliminary study shows the wnt-?-catenin signaling axis and TLR-?-catenin signaling axis are constitutively active in the lamina propria antigen-presenting cells (APCs) and might play an important role in mucosal tolerance. With this perspective, the overarching goal of present proposal is to gain a deeper mechanistic understanding of these two pathways, and how they regulate inflammation, immunological tolerance and vaccine induced immunity in the intestine and systemically. This goal will be accomplished in the following aims: Aim 1: To determine the mechanism mediating constitutive ?-catenin activation in intestinal APCs, and its impact on adaptive immunity. Here, we will determine whether commensals play an instructive role in maintaining constitutive ?-catenin activation in intestinal APCs, and the nature of the innate receptors involved. Furthermore, we will determine the molecular targets of ?-catenin, and the functional consequences of ? -catenin expression in APCs in the intestine. Aim 2: To determine whether ?-catenin activation in APCs regulates the magnitude, quality and persistence of antigen-specific T and B cell responses to oral vaccination. In this aim, we will evaluate how ?-catenin expression in intestinal APCs regulates the innate and adaptive immune response to oral vaccination. Aim 3: To determine whether ?-catenin activation in intestinal APCs regulates self/non-self discrimination and autoimmunity in the gut. This aim will determine the role of ?-catenin activation in intestinal APCs in maintaining the balance between immunity and self tolerance to an intestinal self-antigen. The successful completion of these aims will provide fundamental insights into the mechanisms that maintain the delicate balance between immunity and tolerance, and provide new strategies to control autoimmunity, or to protect against oral infections. PUBLIC HEALTH RELEVANCE: The ability to avoid autoimmunity is a cardinal feature of the immune system. In healthy individuals, this is achieved by several mechanisms of "immunological tolerance," where the immune system acquires unresponsiveness to self antigens, whilst retaining reactivity to foreign microbes. Dendritic cells (DCs) play a key role in maintaining this balance, but the molecular mechanisms by which they do so remain poorly defined. We have identified a novel signaling pathway that imprints a "tolerogenic state" in DCs. The focus of the present proposal is to understand how this signaling pathway in DCs, regulates inflammation, immunological tolerance and vaccine induced immunity.